A lot of people know how to do this, but I'm making this known to all. It's also near-dummy proof... I think?

Part I: Can't Delete What You Can't See
There's multiple ways to go about doing these steps but this will be the fastest and easiest.

- Right-Click on your START button, go up to EXPLORE and select it (meaning left-click)
Here we have Windows Explorer, the meat and potatoes of your Hard Drive. All the junk you've installed, leeched music and videos you've downloaded, and beloved games suchs as EverQuest.
- Select TOOLS at the top and go down to FOLDER OPTIONS... and select the VIEW tab
- Scroll down just a wee bit to where you can see the section with the folder icon labed HIDDEN FILES AND FOLDERS
- Under this section select the radio button next to SHOW HIDDEN FILES AND FOLDERS.
- Below that are two more options. UNCHECK the boxes for HIDE FILE EXTENSIONS FOR KNOWN FILE TYPES and HIDE PROTECTED OPERATING SYSTEM FILES (RECOMMENDED)
- - You still get a warning message when unchecking the second one. It's ok, click YES to continue - -
- It should now look like the picture below
- Click APPLY and OK when you have completed making the changes (if any were made)

Part II: Junk In The Trunk
- Go to C:\Documents and Settings
Here you can see the seperate Windows user accounts. The following steps need to be done to ALL the user accounts. For simplicity reasons I will use the user account "Dashun".
- Go to C:\Documents and Settings\Dashun\Local Settings
- Delete ALL files in the HISTORY folder
- Delete ALL files in the TEMP folder (may need to restart to delete the ones currently in use; ~DFA917.tmp is one I can't delete at the moment)
- Delete ALL files in the TEMPORARY INTERNET FILES folder
Continue doing this for the other user accounts located in the C:\Documents and Settings directory

Part III: Even Windows Has Useless Files Taking Up Space
- Go to C:\WINDOWS\Prefetch and delete all files in that folder
- Go to C:\WINDOWS\Temp and delete all files in that folder
After you have deleted the files in those folders you can now close out WINDOWS EXPLORER and empty your RECYCLE BIN

Part IV: Nearing the End
- Go to your Control Panel (START > SETTINGS > CONTROL PANEL)
- On the left you have an option to either SWITCH TO CLASSIC VIEW or SWITCH TO CATEGORY VIEW. Make sure it says SWITCH TO CATEGORY VIEW so that you are in CLASSIC VIEW (makes things easier).
- Double-click INTERNET OPTIONS
- In the middle area you will see three rectangular buttons: DELETE COOKIES, DELETE FILES, and SETTINGS
- Click the DELETE COOKIES (these are what saves your passwords on websites or tracks what sites you visit) then click OK.
- Next, click the DELETE FILES button. Just click OK this time around.
This step may take a few minutes so be patient if it is.
- Next, click the DELETE FILES button again, but this time check the box for DELETE ALL OFFLINE FILES and click OK
When that is finished you can click OK to close out the INTERNET OPTIONS window, and you can also close out the CONTROL PANEL.

Part V: The End Even Has A Lot of Work
- Go to START > PROGRAMS > ACCESSORIES > SYSTEM TOOLS > DISK CLEAN UP and select it.
You may have to click the DOUBLE ARROWS POINTING DOWN if you do not see what I am talking about. This will expand the full menu to show you programs you haven't used for a certain period of time. Some users will have multiple drives and some will not. That's not the important thing because you will have to do these next steps for ALL drives listed.
- Select your (C:) drive for the time being and click OK
Here you have a list of numerous things. Check a box in each and every single one of those. However, if you have MS OFFICE installed (or the like) and you would like to keep those files for some obsessive-compulsive reason, DO NOT put a check mark in the box for OFFICE SETUP FILES.
- After placing a check in the boxes click OK then YES.
Depending on how often you do this will determine how long this takes. If you've never done this before, you may want to go watch The Lord of the Rings: The Fellowship of the Ring (extended version). It may be done by the time the movie ends. Remeber to do this to ALL drives listed (if you have multiple).

Part VI: The Final Steps I Promise
IF YOU HAVE A SCREENSAVER SET PLEASE DISABLE IT NOW FOR THIS STEP.
- Right-click any where on your desktop where there is an empty space and go down to PROPERTIES.
- Select the SCREENSAVER tab.
- In the drop down list right below SCREEN SAVER select NONE then APPLY and OK.
Now that the better half of your day has gone by cleaning up your computer, the ultimate last step is upon you, defragging. In the same fashion you went to DISK CLEANUP, you will be able to find DISK DEFRAGMENTER. If you have multiple drives you will do this step for every drive, just like in the DISK CLEANUP section.
- Go to START > PROGRAMS > ACCESSORIES > SYSTEM TOOLS > DISK DEFRAGMENTER
- Select (C:) drive and click DEFRAGMENT at the bottom.
If it says it doesn't need to be defragmented or if it says it needs more disk space you may continue at your own risk. I have and nothing bad has happened, but that's my choice. After you have done this for all drives (or some times just one) you can restart your computer and choose to defrag again. I'm obsessive compulsive like that so you never really know if files really are contiguous.

Hope this freed up some space and didn't crash your computer in the process :)